High pyroelectric Ba0.65Sr0.35TiO3 thin films with Ba0.65Sr0.35RuO3 seeding-layer for monolithic ferroelectric bolometer

Ba_0.65Sr_0.35TiO₃ (BST) thin films were deposited by RF sputtering with a very thin Ba_0.65Sr_0.35RuO₃ (BSR) seeding-layer on Pt/Ti/SiO₂/Si substrate. The crystallization of BST thin films and the surface morphology of BSR seeding-layer were characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD patterns show that the BSR seeding-layer affected the orientation of BST thin film, which is highly a-axis textured. It was also found that the BSR seeding-layer had a marked influence on the dielectric properties of BST thin films. Comparing with BST thin films directly deposited on Pt electrode, the dielectric relaxation can be suppressed and dielectric constant increased due to a possible reduction of interface oxygen vacancies at BST/BSR interface. Moreover, J–V measurement indicates that the leakage current density of BST thin films on BSR seeding-layer were greatly reduced compared with that of BST thin films directly on Pt electrodes. The pyroelectric coefficient of BST thin films with BSR seeding-layer is 7.57 × 10⁻⁷ C cm⁻² K⁻¹ at 6 V/μm at room temperature (RT). Our results reveal that high pyroelectric property of BST thin film could be achievable using BSR seeding-layer as a special buffer.     

Structural and electrical properties of crystalline (1−x)Ta2O5−xTiO2 thin films fabricated by metalorganic decomposition

Polycrystalline (1−x)Ta₂O₅−xTiO₂ thin films were formed on Si by metalorganic decomposition (MOD) and annealed at various temperatures. As-deposited films were in the amorphous state and were completely transformed to crystalline after annealing above 600 °C. During crystallization, a thin interfacial SiO₂ layer was formed at the (1−x)Ta₂O₅−xTiO₂/Si interface. Thin films with 0.92Ta₂O₅–0.08TiO₂ composition exhibited superior insulating properties. The measured dielectric constant and dissipation factor at 1 MHz were 9 and 0.015, respectively, for films annealed at 900 °C. The interface trap density was 2.5×10¹¹ cm⁻² eV⁻¹, and flatband voltage was −0.38 V. A charge storage density of 22.8 fC/μm² was obtained at an applied electric field of 3 MV/cm. The leakage current density was lower than 4×10⁻⁹ A/cm² up to an applied electric field of 6 MV/cm.     

Domain wall pinning in polycrystalline perovskite La0.7Sr0.3MnO3

Reversible and irreversible domain wall (DW) motions have been investigated in La_0.7Sr_0.3MnO₃ ceramic samples using frequency-response complex permeability with various amplitudes of AC field. We also examine the effects of temperature in the range from 293 to 368 K and transverse DC magnetic field with a maximum of 4.40×10⁵ A/m on the real part of permeability (μ′). Two relaxations corresponding to reversible wall motions and domain rotations occur in low and high frequency regions, respectively. The irreversible DW displacements can be activated as the amplitude larger than the pinning field of 3 A/m, leading to an increase in μ′. The μ′ obeys a Rayleigh law at the temperature below 343 K or under DC field of less than 4.22×10⁴ A/m. The Rayleigh constant η increases from 5.45×10⁻² to 1.54×10⁻¹ (A/m)⁻¹ as the temperature rises from 293 to 343 K, and η decreases from 5.58×10⁻² to 3.67×10⁻² (A/m)⁻¹ with increasing DC field from 1.99×10³ to 4.22×10⁴ A/m.     

Defect versus nanocrystal luminescence emitted from room temperature and hot-implanted SiO2 layers

Silicon nanocrystals have been synthesized in SiO₂ matrix using Si ion implantation. Si ions were implanted into 300-nm-thick SiO₂ films grown on crystalline Si at energies of 30–55 keV, and with doses of 5×10¹⁵, 3×10¹⁶, and 1×10¹⁷ cm⁻². Implanted samples were subsequently annealed in an N₂ ambient at 500–1100°C during various periods. Photoluminescence spectra for the sample implanted with 1×10¹⁷ cm⁻² at 55 keV show that red luminescence (750 nm) related to Si-nanocrystals clearly increases with annealing temperature and time in intensity, and that weak orange luminescence (600 nm) is observed after annealing at low temperatures of 500°C and 800°C. The luminescence around 600 nm becomes very intense when a thin SiO₂ sample is implanted at a substrate temperature of 400°C with an energy of 30 keV and a low dose of 5×10¹⁵ cm⁻². It vanishes after annealing at 800°C for 30 min. We conclude that this luminescence observed around 600 nm is caused by some radiative defects formed in Si-implanted SiO₂.     

Specific heat of the cubic high-Tc superconductor Ba0·6K0·4BiO3

We report magnetic susceptibility and specific heat measurements on polycrystalline samples of the 30 K superconductor Ba_0·6K_0·4BiO₃. Normal-state magnetization measurements indicate a Pauli-paramagnetic susceptibility of χ_pauli = 2.3 × 10⁻⁵ emu/mole, from which we infer a value for the density of states at the Fermi level of N(0) = 8.6 × 10 ²¹ev⁻¹cm.⁻³ Specific heat measurements performed between 1.6 K and 40 K indicate that considerable lattice softening occurs at low temperatures; the effective Debye temperature drops from 280 K at 35 K to 210 K at 4 K, implying that soft phonon modes are present in this compound. This result indicates that conventional phonon-mediated interactions may be responsible for the high transition temperature exhibited by Ba_0·6K_0·4BiO₃.     

Z-scan determination of the third-order optical nonlinearity of a triphenylmethane dye using 633 nm He–Ne laser

The third-order nonlinear optical response of a triphenylmethane dye (Acid blue 7) was studied using the Z-scan technique with a continuous-wave He–Ne laser radiation at 633 nm. The magnitude and sign of the third-order nonlinear refractive index n₂ of aqueous solution of Acid blue 7 dye were determined; the negative sign indicates a self-defocusing optical nonlinearity in the sample studied. The negative nonlinear refractive index n₂ and nonlinear absorption coefficient β were estimated to be −1.88 × 10⁻⁷ cm²/W and −3.08 × 10⁻³ cm/W, respectively, corresponding to Re(χ⁽³⁾) = −8.35 × 10⁻⁶ esu, and Im(χ⁽³⁾) = −6.88 × 10⁻⁷ esu. The experimental results show that Acid blue 7 dye have potential applications in nonlinear optics.     

The third-order optical nonlinearity of The pyrochlore phase 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 thin film on quartz

The xPb(Mg_1/3Nb_2/3)O₃–(1−x)PbTiO₃ (PMNT) (with x=0.7) thin film is prepared on quartz substrates prepared using a sol–gel process. The PMNT thin film has a well-crystallized pyrochlore phase structure. The sign and magnitude of both real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ of the thin film have been determined by the Z-scan technique performed at 800 nm with a femtosecond laser. The nonlinear refraction index coefficient γ, the nonlinear absorption coefficient β of the thin film are 1.37×10⁻¹² cm²/W and −6.73×10⁻⁸ m/W, respectively. The real and imaginary part of the third-order nonlinear susceptibility of the film are 1.06×10⁻¹⁷ and −1.65×10⁻¹⁹ m²/V², respectively. The results suggested that the nonlinearity is dominated by the refractive for the film.     

Transparent conductive oxide thin films of CdTe-doped indium oxide prepared by pulsed-laser deposition

Transparent conducting oxide thin film CdTe-doped indium oxide (In₂O₃) has been grown by pulsed-laser deposition from a target of CdTe powder embedded in metallic indium. The electro-optical and structural properties were investigated as a function of oxygen partial pressure (PO₂) and substrate temperature (T_s). A film deposited at T_s=420 °C and PO₂=4 Pa shows the minimum resistivity 7.5×10⁻⁴ Ω cm, its optical transmission is 83% and the carrier concentration was 8.9×10²⁰ cm³. The optical band gap and the average roughness of that sample were 3.6 eV and 6.45 Å, respectively. X-ray diffraction studies indicated that the films were polycrystalline. This material is a good candidate for being used as transparent conductor in the CdTe–CdS solar cell.     

Annealing effects on zirconium nitride films

ZrN films were deposited by dc reactive magnetron sputtering on silicon substrates under optimized nitrogen partial pressure of 6×10⁻⁵ mbar. Structural, electrical and optical properties were systematically investigated. Films deposited at room temperature exhibited Schottky structure without any silicide interfacial layer. These films have electrical resistivity of 4.23×10⁻³ Ω cm, which were crystalline in nature, with cubic (1 1 1) orientation. Refractive index and extinction coefficient were found to be 1.95 and 0.43, respectively at a wavelength of 350 nm.

Samples were annealed for 1 h in air at two temperatures, 350 and 550 °C. Scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDAX) showed alloy penetration pits. Extent of penetration was greater in the films, which were annealed at higher temperature (550 °C). Variation in refractive index was observed in the range of 1.95–1.80 at 350 nm, for the annealed films, with increase in grain size from 7.25 to 11.10 nm. Poly-crystalline nature has been observed with (1 1 1) and (2 0 1) orientations. Resistivity is found to increase from 4.23×10⁻³ to 6.21×10⁻³ Ω cm.     

RF-sputtered CrB2 diffusion barrier for Ni/Au Ohmic contacts on p-CuCrO2

Ohmic contacts to p-type CuCrO₂ using Ni/Au/CrB₂/Ti/Au contact metallurgy are reported. The samples were annealed in the 200–700 °C range for 60 s in flowing oxygen ambient. A minimum specific contact resistance of 2 × 10⁻⁵ Ω cm² was obtained after annealing at 400 °C. Further increase in the annealing temperature (>400 °C) resulted in the degradation of contact resistance. Auger Electron Spectroscopy (AES) depth profiling showed that out-diffusion of Ti to the surface of the contact stacks was evident by 400 °C, followed by Cr at higher temperature. The CrB₂ diffusion barrier decreases the specific contact resistance by almost two orders of magnitude relative to Ni/Au alone.     

Sr-doped LaInO3 and its possible application in a single layer SOFC

The effects of dopants on the electrical conductivity of the perovskite-type oxide LaInO₃ have been investigated. Replacement of La by Sr is the most effective way to enhance the conductivity of LaInO₃, whereas Ca substitution for In is rather difficult due to the large difference in the ion radii. The optimum composition is La_0.9Sr_0.1InO_3−δ whose maximum conductivity is 7.6×10⁻³ S cm⁻¹ at 900°C. The electrical conductivity of La_0.9Sr_0.1InO_3−δ has been measured over a wide range of oxygen partial pressure from pO₂=1 to 10⁻²⁵ atm. P-type and n-type behavior at high and low oxygen partial pressure have been observed, respectively, while at intermediate oxygen partial pressures, the electrical conductivity changes only slightly with the oxygen partial pressure. The concept of a single layer solid oxide fuel cell based on a La_0.9Sr_0.1InO_3−δ ceramic pellet has been tested. A maximum power density of 3 mW cm⁻² at 800°C was achieved when dilute H₂ and air were used as fuel and oxidizing agent, respectively.     

Superconducting Nd1.85Ce0.15CuO4 films grown by the pulsed electron deposition technique

Nd_1.85Ce_0.15CuO_4−δ superconducting thin films were prepared on (1 0 0) SrTiO₃ substrates by pulsed electron deposition technique without reducing atmosphere. Oxygen content is finely controlled by high temperature vacuum annealing, and optimal superconductivity has been obtained. The deposition conditions of the film are discussed in details. Higher deposition temperature and lower gas pressure result in the loss of copper and the appearance of the foreign phase Ce_0.5Nd_0.5O_1.75. High quality Nd_1.85Ce_0.15CuO_4−δ epitaxial films are deposited at 840–870 °C in the mixed gas with a ratio of O₂:Ar = 1:3.     

The microscopic features of (Li0.5La0.5)TiO3

In ionic conducting materials, the crystal structure is closely related to the ionic conductivity. In this research we studied the microscopic features of Li_0.5La_0.5TiO₃ which exhibited a lithium ionic conductivity as high as 1×10⁻³ Scm⁻¹ at room temperature by XRD, TEM and SIMS. It was found that the superstructure was caused by the ordering of La⁺³ and vacancy, producing the 2a_p×2a_p×2a_p unit cell. This ordering was found to be regular in microscopic region, but became irregular in macroscopic region. Li⁺ showed a random distribution which meet the needs for the fast ionic conduction. The second phase was found to be Li₂TiO₃ which existed in the grain boundary junctions.     

Structural and electrical characterisation of La0.5Ca0.5MnO3 thin films grown by pulsed laser deposition

Thin films of perovskite manganite, with nominal composition La_0.5Ca_0.5MnO₃, have been prepared by pulsed laser deposition on (1 0 0) SrTiO₃, (1 0 0) LaAlO₃, (1 0 0) Si and YSZ/CeO₂-buffered (1 0 0) Si substrates. Structural and electrical characterisation was performed on the films. The magneto-transport properties of all the thin films depart from the bulk behaviour. The LCMO film grown on buffered Si shows an insulator–metallic transition around 130–150 K while the one deposited directly on Si displayed a similar behaviour under a melting field of 1 T. However, that transition is absent in the films grown on LAO and STO. We suggest that appropriate stress values induced by the substrate favour the formation of metallic percolative paths.     

Preparation of tantalum oxide thin films by photo-assisted atomic layer deposition

Tantalum oxide thin films were prepared by photo-assisted atomic layer deposition (Photo-ALD) in the substrate temperature range of 170–400 °C using Ta(OC₂H₅)₅ and H₂O as precursors. The constant growth rates of 0.42 and 0.47 Å per cycle were achieved for the films grown by normal ALD and Photo-ALD, respectively. The increased growth rate in Photo-ALD is probably due to the reactive surface by photon energy and faster surface reaction. In Photo-ALD, however, the constant growth rate started at lower temperature of 30 °C and one cycle time shortened up to 5.7 s than that of normal ALD. The films grown by normal ALD and Photo-ALD were amorphous and very smooth (0.21–0.35 nm) as examined by X-ray diffractometer and atomic force microscopy, respectively. Also, the refractive index was found to be 2.12–2.16 at the substrate temperature of 190–300 °C, similar to that of the film grown by normal ALD. However, the remarkably low leakage current density of 0.6×10⁻⁶ A/cm² to 1×10⁻⁶ A/cm² at applied field of 1 MV/cm is several order of magnitude smaller than that of normal ALD, probably due to the presence of reactive atom species.     

Corrosion monitoring of stainless steel 304L in lithium bromide aqueous solution using transmittance optical detection technique

We report a method based on the power ratio of transmittance for monitoring the corrosion rate in stainless steel 304L immersed in an aqueous solution of lithium bromide at 50 wt%, at 70 °C. The optical transmittance measured in the solution contaminated with corrosion oxides at different times of exposure is related to the physical degradation of the stainless steel samples. Lasers at 532 and 632 nm were utilized for monitoring the accumulation of corrosion oxides dissolved in the lithium bromide solution of the metallic samples for 480 h. The change in the optical power of transmittance was 13 μW/480 h measured at 532 nm and 3.6 μW/480 h at 632 nm. The variation of the power ratio for 532 nm was from 0.01 to 0.24, and for 632 nm, from 0.01×10⁻³ to 15.61×10⁻³; this is proportional to an accumulated corrosion rate of [0.0142×10⁻³–0.552×10⁻³ g/cm²] for an exposure time of 432 h.     

Chemically deposited copper oxide thin films: structural, optical and electrical characteristics

Thin films of copper oxide with thickness ranging from 0.05–0.45 μm were deposited on microscope glass slides by successively dipping them for 20 s each in a solution of 1 M NaOH and then in a solution of copper complex. Temperature of the NaOH solution was varied from 50–90°C, while that of the copper solution was maintained at room temperature. X-ray diffraction patterns showed that the films, as prepared, are of cuprite structure with composition Cu₂O. Annealing the films in air at 350°C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.1 eV (direct) to 1.75 eV (direct). The films show p-type conductivity, 5×10⁻⁴ Ω⁻¹ cm⁻¹ for a film of thickness 0.15 μm. Electrical conductivity of this film increases by a factor of 3 when illuminated with 1 kW m⁻² tungsten halogen radiation. Annealing in a nitrogen atmosphere at temperatures up to 400°C does not change the composition of the films. However, the conductivity in the dark as well as the photoconductivity of the film increases by an order of magnitude. The electrical conductivity of the CuO thin films produced by air annealing at 400°C, is high, 7×10⁻³ Ω⁻¹ cm⁻¹. These films are also photoconductive.     

Oxygen transfer processes in (La,Sr)MnO3/Y2O3-stabilized ZrO2 cathodes: an impedance spectroscopy study

Impedance spectroscopy was used to study the oxygen reaction kinetics of La_0.8Sr_0.2MnO₃ (LSM)-based electrodes on Y₂O₃-stabilized ZrO₂ (YSZ) electrolytes. Three types of electrodes were studied: pure LSM, LSM–YSZ composites, and LSM/LSM–YSZ bilayers. The electrodes were formed by spin coating and sintering on single-crystal YSZ substrates. Measurements were taken at temperatures ranging from 550 to 850°C and oxygen partial pressures from 1×10⁻³ to 1 atm. An arc whose resistance R_el had a high activation energy, E_a=1.61±0.05 eV, and a weak oxygen partial pressure dependence, (P_O2)^−1/6, was observed for the LSM electrodes. A similar arc was observed for LSM–YSZ electrodes, where R_el(P_O2)^−0.29 and the activation energy was 1.49±0.02 eV. The combination of a high activation energy and a weak P_O2 dependence was attributed to oxygen dissociation and adsorption rate-limiting steps for both types of electrodes. LSM–YSZ composite cathodes showed substantially lower overall interfacial resistance values than LSM, but exhibited an additional arc attributed to the resistance of YSZ grain boundaries within the LSM–YSZ. At 850°C and low P_O2, an additional arc was observed with size varying as (P_O2)^−0.80 for LSM and (P_O2)^−0.57 for LSM–YSZ, suggesting that diffusion had become an additional rate limiting step. Bilayer LSM/LSM–YSZ electrodes yielded results intermediate between LSM and LSM–YSZ. The results showed that most of the improvement in electrode performance was achieved for a LSM–YSZ layer only ≈2 μm thick. However, a decrease in the grain-boundary resistance would produce much better performance in thicker LSM–YSZ electrodes.     

Low-field negative magnetization and coercive-field magnetization reversal in transition metal chalcogenides; Cr2FeSe4 magnetic structure from neutron diffraction

Low-field negative magnetization, of the order of −10⁻¹ emu/g-Oe, from 4.2 K up to room temperature and higher (350 K), and coercive-field magnetization reversal are both present in Cr_(3−x)Fe_xX₄ for X=S, Se, Te and x=0 to 3, and for Cr₅Te₈ and Cr₇Te₈. For Cr₂FeSe₄ the zero-field-cooled (ZFC) magnetization is negative for 5 Oe and below. To obtain a more detailed knowledge of the magnetic phases involved in the observed magnetization versus temperature M(T) curves, we obtained and studied neutron diffraction (n.d.) scans on the compound Cr₂FeSe₄, taken at 14 temperatures from 4.2 to 300 K. For this same n.d. sample, the temperature for magnetization reversal of value −3×10⁻⁴ emu/g-Oe is 80 K in 40 Oe applied field, then the reversal disappears for 65 Oe applied field. The complex magnetic interactions responsible for this reversal are revealed in the hysteresis curves.     

MnO thin film cathode for rechargeable microbatteries

Thin films of MnO were deposited by electron beam evaporation using a MnO or MnO₂ source. The thin films were charaterized by X-ray and electron diffraction. The Coulomb titration curve reveals a potential plateau of 2.9 V over the composition range 0.05<x<2.0. The chemical diffusion coefficient of lithium in thin films at 15°C is 2.7×10⁻¹⁴ cm²/s for 0<x<0.01 and 2.2×10⁻¹⁵ cm²/s for 0.02<x<0.06. Good reversibility for lithium insertion and extraction is demonstrated by cyclic voltammetry.